The tornado that killed six people and wrecked much of La Plata last week has lost its ranking as Maryland's first F5 storm - the most powerful category.
After a four-day inspection of damage along the storm's 68-mile track, a team of experts assembled by the National Weather Service gave it a final rating yesterday of 4 on the Fujita Tornado Damage Scale, with top winds of 260 mph in the La Plata area. A preliminary assessment of the storm's power, released the day after it struck, had rated it an F5, with winds of 261 mph or more.
"Just because we're calling it an F4 instead of an F5 does not mean it wasn't a bad tornado," said John E. Ogren, meteorologist-in-charge at the weather service's Indianapolis forecast office, who led the assessment team. "It was a terrible tornado.
"F4 and F5 tornadoes are only 2 percent of tornadoes, and that 2 percent of tornadoes cause 70 percent of the fatalities," he said.
Maryland has recorded two other F4s. The first was the storm Nov. 9, 1926, in La Plata that killed 17 people, all but three of them schoolchildren. The second was a twister June 2, 1998, in Frostburg. It destroyed 30 homes and businesses and caused $5 million in damage, with five minor injuries.
Ogren's team included a Fort Worth, Texas, forecaster with extensive tornado experience, and a wind engineer with expertise in storm damage.
A characteristic that distinguishes an F5 tornado from an F4 is that F5s will lift even well-built houses from their foundations and carry them away. The first assessment team sent to La Plata, the day after the storm, based its F5 ranking in part on the observation that "at least six homes were completely wiped off their foundation."
On closer inspection, Ogren's team found that the houses were not well-fastened.
"So, they could be destroyed at lesser wind speeds than other homes that are well-connected," Ogren said.
The team also found that some of the most severe structural damage in downtown La Plata was caused by hurtling debris, and not by wind alone.
Ogren said a lumberyard was blown away by tornadic winds estimated at F2 or F3 strength - between 113 mph and 206 mph. "Steel beams from the lumberyard were blown several hundred yards into the orthodontist's office," he said. The beams caused damage initially misread as evidence of F5 winds.
The only F5 tornado recorded on the East Coast remains a 1953 storm that struck in Worcester, Mass., killing 94.
The tornado that struck College Park and Laurel on Sept. 24 was rated an F3 along portions of its track. It killed two people and caused $73 million in damage.
Gov. Parris N. Glendening put last week's storm damage at $120 million. But his deputy chief of staff, Gene Lynch, said: "It's not a hard estimate. The governor was repeating numbers he had heard from others. There has not been a definitive number for the total damage."
The Maryland Emergency Management Agency has estimated $5.8 million in damage to public infrastructure alone.
Members of the Senate Budget and Taxation and House Appropriations committees toured some of the destruction yesterday in La Plata.
"It was a chance for us to see the scale of what needs to be aided," said Sen. Barbara A. Hoffman, a Baltimore Democrat and chairwoman of the Senate committee.
The committee approved in concept the governor's proposed $3.1 million in aid to local governments, and uninsured homeowners and businesses. Members will take a formal vote after Glendening provides specifics on spending, Hoffman said.
Sun staff writer Howard Libit contributed to this article.